Lead enters aquatic systems from runoff or as fallout of insoluble precipitates and is found in sediments. Typical fresh-water concentrations are between 1 and 10 g/1 while natural lead concentrations in soil range from 2 to 200 ppm and average 10 to 15 ppm. . Deep ocean waters, below 1000 m, contain lead at 0.02 to 0.04 มิวกรัม/kg concentrations, in contrast, surface waters contain from 0.2 to 0.35 มิวกรัม/kg. Besides, drinking water concentrations of lead may be greatly increased in soft-water area through corrosion of lead- lined piping and connections.